DC (direct current) to DC converters are circuits often used to boost a DC voltage, such as may be provided by a battery, to a higher level necessary for the operation of other circuitry. In a common prior art DC to DC converter, an inductor is placed in series with a solid-state switch across a battery. The solid-state switch is activated by a control circuit to periodically conduct current through the inductor, then to open, causing the inductor to produce a high voltage pulse at the junction of the solid-state switch and the inductor. This pulse may be received by a rectifying diode to charge an accumulating capacitor. The voltage on the capacitor is feedback to the control circuit which repeats the charging and interrupting cycle of the inductor until the desired voltage level is produced on the capacitor.
Such DC to DC converters are essential for operating many modern devices such as pagers, cell phones and medical monitors on low voltage battery sources.
Whenever batteries are used in a circuit, the risk of improper battery insertion is present. Improper insertion of a battery may reverse the polarity on the DC to DC converter and thus may damage the DC to DC converter or cause premature drainage of the battery. For this reason, it is known to use battery holders which do not allow the battery to be connected with reverse polarity. Typically, these battery holders include insulating spacers which s prevent contact between the battery terminals and the battery holder terminals when improper insertion has occurred. Unfortunately, with these types of battery holders, improper insertion prevents the device from working at all, even though the circuit has been protected.
It is known that inserting a diode bridge rectifier between the battery and the DC to DC converter will allow the connection of the battery in either polarity. Such a diode bridge, however, is impractical for DC to DC converters which use a single battery cell providing approximately 1.5 volts of input voltage. The diodes of the bridge may cause a voltage drop of as much as 1.4 volts of the available battery voltage.